A new method for generating stage-discharge relations (rating curves) for geomorphically stable channels is presented and applied to two streams in the Whitewater River basin, Kansas. The approach converts measurements of stage into discharge using a fluid mechanically based model. The model does not use empirical roughness coefficients, such as Manning coefficients, but rather determines channel roughness from field measurements of the (1) channel geometry, (2) the physical roughness of the bed, banks, and floodplain, and (3) the vegetation density on the banks and floodplain. These measurements are used to calculate explicitly the drag on the small-scale topographic features on the boundary, the drag on the stems and branches of woody vegetation, and the friction on the bed, banks, and floodplain. The theoretical rating curves produced by the model for two study reaches, which are near U.S. Geological Survey (USGS) streamflow-gauging stations, are in good agreement with direct measurements of discharge made by the USGS. Our method has the potential of providing accurate estimates of stream flows less expensively than conventional gauging methods. In addition, the method can be used to obtain more accurate discharge estimates than conventional indirect methods for determining discharge, which are based on estimates of Manning's coefficient.